Tony R Montgomery Jr1, Alex Olmos1, Kylie N Sears1, Pasquale J Succi2, Shane M Hammer1, Haley C Bergstrom2, Ethan C Hill3, Michael A Trevino1 and Taylor K Dinyer-McNeely1

1Oklahoma State University, Stillwater, OK

2University of Kentucky, Lexington, KY

3University of Central Florida, Orlando, FL

Blood flow restriction (BFR) has been shown to trap metabolites in the muscle, which influences factors underlying force production. Motor unit mean firing rates (MFR) and action potential amplitude (MUAPAMP) can be unveiled with surface electromyography (EMG) decomposition. It is unclear if BFR influences the relationships between MUAPAMP and MFR vs. recruitment threshold (RT) during isometric contractions performed to task failure. PURPOSE: To determine the effects of BFR on the MFR and MUAPAMP vs. RT relationships during fatiguing isometric elbow flexions. METHODS: 10 men (24.5±4.0 yrs) performed isometric trapezoidal contractions at 50% maximum voluntary contraction to task failure with or without BFR, on 2 separate days. For BFR, a cuff was inflated to 60% of the pressure required for full brachial artery occlusion at rest. During both visits, surface EMG was recorded from the biceps brachii of the dominant limb and the signal was decomposed. Y-intercepts and slopes were calculated for the MUAPAMP and MFR vs. RT relationships. A paired samples t-test was used to determine the number of repetitions completed between BFR and CON. ANOVAs (repetition [first, last] × condition [BFR, CON]) were used to determine differences in MFR vs. RT and MUAPAMP vs. RT relationships. RESULTS: Participants completed more repetitions during CON (12±4) than BFR (9±2; p=0.012). There was no significant interaction (p>0.05) between the slopes and y-intercepts during the repetition × condition interaction for MUAPAMP vs. MFR. However, there was a main effect of repetition for the slopes of the MUAPAMP vs. RT (p=0.041) but not the y-intercept (p=0.964). Post-hoc analysis (collapsed across condition) indicated the slopes of the MUAPAMP vs. RT during the first repetition was less than the last repetition (first: 0.022±0.003 mv/%MVC; last: 0.028±0.004 mv/%MVC; p=0.041). There was no significant interaction (p>0.05) between the slopes and y-intercepts MFR vs RT. CONCLUSIONS: BFR resulted in the same amount of higher threshold MU recruitment in approximately 75% of the repetitions (12 reps for CON vs 9 reps for BFR). Further, there was no change in MFR for either condition, even when taken to task failure. Thus, BFR training may create similar MU responses with less total work completed than training without BFR.

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